Increased sophistication in high speed engines has resulted in the generation of high temperatures between meshed gears and their rotatable mounts, specifically, bearing assemblies. In order to reduce this heat, a flow of oil is applied to the gears and bearings to dissipate the heat as well as lubricate the interfaces of the components. As a result of the high speed operation of the components, conductively heated oil is churned and thereby further mechanically heated as it circulates about the bearing assembly. This oil tends to be the cause of excessive heating within the bearing. Thus, while oil may be a desirable coolant in many instances, churning resulting from direct contact with rotary elements diminishes its cooling efficiency.
In order to isolate a cooling flow of oil from rotating elements to avoid churning, a number of proposals have been disclosed. One prior art proposal, contained in U.S. Pat. No. 4,222,705 to Smith issued Sept. 16, 1980, includes the use of a heat conductive fluid trapped within a tapered annular cavity which, in turn, rotates with a housing structure. Due to centrifugal action, the fluid is repeatedly pumped to opposite ends of the cavity where it is alternatively vaporized and recondenses such that heat is transferred away from an inner bearing race. This self-contained design does not provide means for drawing the heated oil away from the bearing for external cooling, nor is the issue of lubrication addressed in any way.
Ando, U.S. Pat. No. 4,137,997, issued Feb. 6, 1979, discloses the use of cooling oil which is circulated about an outer race of spindle bearings by means of circumferential cooling passages and pressure lubrication of the bearing by means of an isolated flow of lubricating oil. Ando does not show cooling of an inner bearing race nor means of simply pumping the lubricating flow through the bearing.
One arrangement has been proposed in which an inner bearing race is mounted on a hollow sleeve which, in turn, defines an internal cavity extending axially along a shaft. U.S. Pat. No. 3,706,483 to Irwin discloses such a structure. The cavity is filled with a heat conductive material which draws heat away from the inner bearing race and toward heat dissipating fins. Lubrication of the bearing is not provided for.
In order to both dissipate heat within the bearing assembly and provide a lubricating flow without risk of inducing excess heating, one could imagine utilizing a single flow of oil and limiting the amount of oil admitted within the bearing, thereby allowing the excess oil to provide a cooling wash to the outside of the assembly while subjecting only a minimal flow of oil to the rotating bearing elements. One approach would be to provide lubricating passages of reduced dimension, whereby the amount of oil admitted with the bearing is restricted. Test results indicate that in order to reduce the dimension of such passages to a level at which excessive churning is effectively precluded, the passages would necessarily be reduced to a dimension at which oil passing therethrough would easily plug the orifice. The resulting lack of lubrication could result in catastrophic failure of the machine. Hence, such a solution is not practical.
The present invention is directed to overcoming one or more of the above problems.